Exceptional fossil preservation in the Comley Lagerstätte, Shropshire: testing the phylogeny of Early Cambrian animals

“寒武纪大爆发”是地球生物圈多样性的巨大扩张，在地质记录中第一次被广泛的动物化石证据所见证。事实上，寒武纪化石对于追踪现代动物群体的组装路径至关重要。大多数寒武纪化石只保留了它们的硬骨骼组织，而对于评估分类关系至关重要的软体形态学的重要细节通常会丢失。然而，有一些著名的寒武纪化石地点，其中保存了软组织。在这种情况下，“奥斯滕”风格的保存提供了一系列蠕虫和节肢动物的极其精细的解剖细节（亚微米级）。来自“奥斯滕”矿床的化石证据对于研究动物身体计划的早期发展至关重要，特别是甲壳类动物，这一点特别重要，因为昆虫和大多数活的动物多样性都是在这个群体中出现的。“奥斯滕”式化石保存主要限于中、晚寒武世和早奥陶世。“奥斯滕”保存发生的过程尚不完全清楚，但涉及矿物磷酸钙对软组织的快速浸渍或结壳。这些过程必须足够快，以在它们腐烂之前保存脆弱的结构，如触角，嘴巴部分和三维微米级的毛发。“奥斯滕”化石保存得如此完整，以至于它们的解剖细节可以与现代动物进行直接比较。尽管世界范围内寒武纪岩石中的“奥斯滕”保存现象普遍存在，但有关动物化石的许多基本问题仍然存在：这些组合中的幼年生物在多大程度上为早期动物的解剖和进化，特别是蜕皮动物和节肢动物的进化提供了一个窗口;这些生物群是原始海洋生物群落的“快照”，还是偏向于某些动物群体;这些早期动物生活在什么样的海洋环境中？该项目将调查岩石记录中保存的最古老的“奥斯滕”动物。这些化石来自什罗普郡下寒武纪岩石中一个特殊的化石保存地点，即约5.11亿年前的科姆利石灰岩。这些碳酸盐沉积在延伸到威尔士的古代海洋盆地的浅边缘。它们产生的年龄诊断三叶虫，允许与全球地层的相关性。一项针对约5公斤岩石的有限的试点研究表明，科姆利石灰岩是“奥斯滕”生物的来源，这是英国唯一的这种保存方式。科姆利石灰岩是一个潜在的，但目前尚未开发的水库，早期动物的化石。要实现其全部潜力，需要从什罗普郡碳酸盐岩序列的关键层位挖掘100公斤岩石。我们将对来自科姆利的新化石材料和来自斯堪的纳维亚半岛和其他地方的比较材料进行详细的扫描电子显微镜检查。这将提供有关寒武纪动物解剖细节的新信息，这将大大有助于蜕皮动物和节肢动物关系的研究。这些化石还将用于测试有关矿物磷酸钙如何复制具有复杂三维细节的动物组织的假设，以及这个过程是否偏向于特定的动物群体或软组织。我们将评估寄主岩石的岩相学，再加上地球化学分析，以帮助确定其环境和成岩历史。总的来说，这些数据可以用来确定“奥斯滕”的海洋环境，保存了哪些化石，以及它们对动物进化的更广泛意义。

The 'Cambrian explosion' was a huge expansion in the diversity of Earth's biosphere, witnessed, for the first time in the geological record, by widespread fossil evidence of animals. Indeed, Cambrian fossils are of pivotal importance for tracking the pathways that allowed the assembly of the modern animal groups. Most Cambrian fossils preserve only their hard skeletal tissues, while important details of soft body morphology, critical for assessing taxonomic relationships are usually lost. However, there are a number of celebrated Cambrian fossil localities where fossilised soft tissues are preserved. In this context, the 'Orsten' style of preservation provides extremely fine anatomical detail (to sub-micron level) of a range of worm and arthropod animals. The fossil evidence from 'Orsten' deposits is critical for investigating the early development of animal body plans, particularly crustaceans, and this is of particular importance given that insects and therefore the majority of living animal diversity arose within this group. 'Orsten' style fossil preservation is mainly limited to rocks of Middle and Late Cambrian, and Early Ordovician age. The processes by which 'Orsten' preservation occurs are incompletely known, but involve the rapid impregnation or encrustation of soft tissues by the mineral calcium phosphate. These processes must be rapid enough to preserve fragile structures such as antennae, mouth parts and micron-scale hairs in 3-dimensions before they could decay. So completely preserved are 'Orsten' fossils that their anatomical detail allows direct comparison with modern animals. Despite the worldwide occurrence of 'Orsten' preservation in Cambrian rocks, many fundamental questions about the fossil animals remain: to what degree do the juvenile organisms in these assemblages provide a window on the anatomy and evolution of early animals, especially ecdysozoan and arthropod evolution; why and how is the soft anatomy preserved; are the assemblages a 'snapshot' of the original marine community or are they biased towards certain animal groups; and what types of marine environments did these early animals occupy? This project will investigate the oldest 'Orsten' animals preserved in the rock record. The fossils are from a site of exceptional fossil preservation in the Lower Cambrian rocks of Shropshire, the Comley Limestones, which are about 511 million years old. These carbonates were deposited on the shallow margins of an ancient marine basin that extended into Wales. They yield age diagnostic trilobites that allow correlation with global stratigraphy. A limited pilot study, targeting about 5 kg of rock has shown that the Comley Limestones are a source of 'Orsten' organisms, the only instance of this style of preservation in the UK. The Comley Limestones are a potential, but presently untapped reservoir of fossilized early animals. Realising their full potential requires excavation of 100s kg of rock from the key horizon in the carbonate sequence of Shropshire. We will conduct detailed scanning electron microscopy of new fossil material from Comley and comparative material from Scandinavia and elsewhere. This will provide new information about the anatomical detail of Cambrian animals that will contribute greatly to the study of ecdysozoan and arthropod relationships. The fossils will also be used to test hypotheses about how the mineral calcium phosphate can replicate animal tissues with intricate 3-dimensional detail and whether this process is biased to particular animal groups or soft tissues. We will evaluate the petrography of the host rocks, coupled with geochemical analysis, to help determine their environmental and diagenetic history. Collectively these data can be used to identify the marine setting of the 'Orsten', what fossils are being preserved, and their wider significance for animal evolution.